This invention relates to power division and combination, and more particularly to power divider/combiners usable at radio frequencies including microwave and millimeter-wave frequencies.
Modern communications often require broad bandwidth transmissions in order to accommodate very high data rates. These transmissions are made using electromagnetic or light signals. Regardless of the form of the transmission, substantial electronic amplifier power is often required at the transmitting end of a transmission path. If the transmission is by way of electromagnetic transmission lines, the lines are subject to significant losses at the high frequencies implied by broad bandwidth, and reamplification may be required at various points along the path. If the transmission path includes free-space propagation from one antenna to another, the transmission losses can be significant, which requires significant transmitted power to maintain the received signal above ambient noise levels. The production of photonic signals by means of lasers or other optoelectric devices is subject to significant inefficiencies. All of the losses and inefficiencies, in turn, require that electronic power amplification be performed.
As solid-state devices have improved over the years, the amount of power which an individual solid-state device can produce within a given frequency band has increased. As a result, a power level at a given frequency band which at one time might have required the paralleled outputs of several solid-state devices may now require only one solid-state device. However, with each advance in the power-handling capability of solid-state devices, the requirements of power, frequency and bandwidth have also increased, so that there is continuing need for electronic power amplifiers. The higher frequency and bandwidth requirements, in turn, tend to make parasitic reactances more important, and to require that the structures of the amplifiers become smaller, notwithstanding that the power requirements are remain high. Thus, in this context, the term xe2x80x9cpowerxe2x80x9d means that more than one solid-state device is required to produce the total output power of the amplifier, regardless of the actual power level.
The paralleling of amplifiers is old in the art. For example, vacuum-tube audio amplifiers using push-pull output stages were common at one time, and continue to find niche applications. Cable-television and similar amplifiers operating in the frequency range from about 50 to about 220 MHz. using both simple paralleled stages and push-pull amplifier stages, have been in use for forty years, and are known in the art. Such cable television amplifiers were generally fabricated in the form of discrete-component assemblages on printed-circuit boards.
The paralleling of two amplification devices ordinarily requires the division of the signal to be amplified into two portions, application of each portion of the signal to be amplified to one of the two amplifier devices, and the combining of the amplified output signals from the two devices. In general, signal dividers and signal combiners are passive devices which use the same types of structure, so that a signal divider for use at a given frequency and power level can generally be used as a signal combiner, and similarly a signal combiner can generally be used as a signal divider, simply by reversing the input and output ports. Those skilled in the art know that the phasing of the signals to be combined must be made in such a manner as to prevent cancellation, and that phase can be controlled at any location between the division of the signal into two portions and the combining point.
Power division in the abovementioned cable television amplifiers was generally done in one of two ways, namely by a pair of resistive power dividers coupled to the signal source, with their taps coupled to the divided-signal utilizing apparatuses, or by a center-tapped hybrid transformer arrangement wound on a magnetic core, with the center tap coupled to the source and the ends of the windings coupled to the divided-power utilization devices. It is common, in such arrangements, to couple an isolation resistor across the divided-power ports. It should be noted that the resistive power divider is lossy, in that half of the signal power is wasted as heat in the resistors, so the less lossy center-tapped hybrid was used almost exclusively for power combining.
In the field of microwave power amplification, U.S. Pat. No. 4,701,716, issued Oct. 20, 1987 in the name of Poole describes a scheme for paralleling distributed amplifiers such as travelling-wave tubes in such a manner as to maximize the bandwidth of the resulting combined system. In the Poole arrangement, distributed microwave 3 dB hybrids in the form of coupled quarter-wave transmission lines are used for the power dividers and combiners. Such distributed transmission-line hybrid arrangements are well known in for use in microwave systems.
While paralleling two output devices can provide about a doubling of the amplifier output power for a given level of distortion, yet more power may be required for certain applications. For such higher-power applications, the paralleling of more than two devices may be required. U.S. Pat. No. 4,315,222, issued Feb. 9, 1982 to Saleh describes a power combiner arrangement in which the output power from a plurality of amplifier modules is combined at a single junction. Each amplifier is coupled to the junction by a transmission line having an electrical length of one quarter wavelength (xcex/4) at a frequency within the operating frequency range. U.S. Pat. No. 4,755,769, issued Jul. 5, 1988 in the name of Katz describes a composite amplifier including four signal amplifiers. A four-way power divider divides the signal to be amplified into four equal-amplitude, equal-phase portions, and each of the portions is applied to the input port of one amplifier. The amplified output signals are combined at a combining port by way of a scheme using the impedance transformation attributes of quarter-wavelength transmission lines. While details of the power divider are not specified in the Katz patent, one possible scheme for four-way power division is an arrangement similar to his combining arrangement, namely a cascade of two stages of transmission-line segments, including a first stage of division into two signal portions, followed (in the direction of the flow of signal in such an amplifier) by a second stage of division into two parts of each of the two divided signals, for a total of four divided signals.
Power division and combination can be performed by simple connection of two or more load or source devices, respectively, to a common source or load, respectively. Such simple junction-type splitter/combiners suffer from the problem of impedance mismatch, which tends to cause a portion of the input signal power to be reflected rather than going to the output ports of the splitter/combiner. A paralleled power amplifier generally similar to the Katz paralleled amplifier is described in U.S. Pat. No. 4,780,685 issued Oct. 25, 1988 in the name of Ferguson. The Ferguson arrangement uses tapped transmission lines as impedance transformers to improve the impedance match between a common 50-ohm output transmission line and plural transmission lines combined at a combining node.
An arrangement for combining a large number of individual amplifier modules into a composite microwave amplifier is described in U.S. Pat. No. 4,641,106, issued Feb. 3, 1987 in the name of Belohoubek et al. In the Belohoubek arrangement, radial transmission lines with quarter-wavelength slots are used for the division of the signal to be amplified into plural portions, and also for combining of the amplified signals. The Belohoubek et al. arrangement includes isolation resistors coupled between each individual transmission path and the next.
Another arrangement for combining a large number of amplifiers is described in U.S. Pat. No. 4,965,530, issued Oct. 23, 1990 in the name of Katz. In the Katz ""530 arrangement, the output ports of each paralleled amplifier are coupled to a common combining node by way of switched transmission lines and switched isolation resistors.
Improved paralleling arrangements are desired.
A power splitter/combiner according to an aspect of the invention, for dividing applied electromagnetic signals into plural substantially equal portions, includes a plurality, equal in number to the number of the substantially equal portions, of cascades of artificial transmission line sections. Each of the cascades includes an xe2x80x9cinputxe2x80x9d port and an xe2x80x9coutputxe2x80x9d port, with it being understood that the terms xe2x80x9cinputxe2x80x9d and xe2x80x9coutputxe2x80x9d are reversed when the splitter/combiner is operating as a combiner. Each of the cascades also includes at least a first section of artificial transmission line coupled its input port and has a node remote from the input port, and a last section of artificial transmission line connected to the output port and has a node remote from the output port. Each of the cascades includes a further coupling arrangement coupling the node of the first section of artificial transmission line to the node of the last section of artificial transmission line of that cascade. The further coupling arrangement may comprise one of (a) a simple connection of the node of the first section of artificial transmission line to the node of the last section of artificial transmission line, so that the cascade includes but two sections of artificial transmission line, and (b) at least an additional or further artificial transmission line including input and output nodes, where one of which nodes of the further artificial transmission line is connected to the node of the first section of artificial transmission line. An input coupling arrangement is coupled to the input ports of the plurality of cascades of artificial transmission lines, for coupling the input ports of the plurality of cascades in parallel to define a common port of the power splitter/combiner. The electromagnetic signals, if applied to the common port of the power splitter/combiner, divide in accordance with the impedances presented by the input ports of the cascades. Similarly, the individual electromagnetic signals from the cascades, if combined at the common port of the power splitter/combiner, combine in accordance with the impedances presented to the common port.
The power splitter/combiner also includes a plurality, equal in number to the number of stages of artificial transmission line cascaded in any one of the cascades of artificial transmission lines, of sets of equal-valued isolation resistors. One of the sets of equal-valued isolation resistors is coupled to the output ports of the cascades and to a node common to the one of the sets. One end of the resistors of each other set of the plurality of sets of equal-valued isolation resistors are coupled to a node common to that set The other ends of the resistors of each other one of the sets of equal-valued resistors are also coupled to the nodes of corresponding ones of the stages of the artificial transmission lines remote from the input port of that one of the cascade of artificial transmission lines in which the stages of the artificial transmission lines lie.
Each of the stages of artificial transmission line, in an advantageous manifestation of the invention, includes at least first and second planar spiral inductors overlying a ground plane. The first and second planar spiral inductors are electrically coupled in series, and at least one of the stages of artificial transmission line of each cascade further includes first, second and third discrete capacitors coupled to the ends of the spiral inductors. In a particular embodiment, each of the discrete capacitors is in the form of a capacitive metallization overlying the ground plane, and the splitter/combiner includes four cascades of artificial transmission lines.
In a particular embodiment of the splitter/combiner, the input coupling arrangement comprises a first pair of elongated transmission lines in the form of strip conductors overlying the ground plane, where each transmission line of the first pair of elongated transmission lines has a first predetermined length, and are coupled together at a first common node for receiving the electromagnetic signal. The input coupling arrangement also includes a second pair of elongated transmission lines, also in the form of strip conductors overlying the ground plane. Each transmission line of the second pair of elongated transmission lines has a second predetermined length different from the first predetermined length, and they are coupled together at a second common node. A transmission-line bridge couples the first common node of the first pair of transmission lines to the second common node of the second pair of transmission lines, to thereby define the common port of the splitter/combiner. Thus, electromagnetic energy applied to the common port of the splitter/combiner arrives at the first common node is also applied to the second common node.
In another avatar of the invention, a power splitter/combiner for dividing applied electromagnetic signals into plural substantially equal portions, or for combining plural electromagnetic signals, comprises first, second, third and fourth cascades of artificial transmission lines or artificial transmission line segments or sections. Each of the cascades of artificial transmission lines includes a cascade of first, second and third artificial transmission line sections. Each of the artificial transmission line sections defines first and second nodes, and, within any one of the cascades of artificial transmission line sections, the second node of the first artificial transmission line section is connected to the first node of the second artificial transmission line section, and the second node of the second artificial transmission line section is coupled to the first node of the third artificial transmission line section.
In one hypostasis of this other avatar, a power coupling arrangement includes a common port for, in one mode of operation, receiving the electromagnetic signals, and routing divided electromagnetic signals with substantially equal amplitude and phase to the first nodes of the first artificial transmission line sections of the first, second, third and fourth cascades of artificial transmission line sections. Each of the first, second and third artificial transmission line sections of any one of the first, second, third and fourth cascades of artificial transmission line sections includes first and second planar, spiral conductors overlying a ground plane, with a second end of the first planar, spiral conductor of any one of the artificial transmission line sections connected to a first end of the second planar, spiral conductor of the one of the artificial transmission line sections. As a result, a first end of the first planar, spiral conductor defines the first node of the one of the artificial transmission line segments, and a second end of the second planar, spiral conductor defines the second node of the one of the artificial transmission line segments.
This other avatar also includes first, second, and third sets of isolation resistors, each containing four isolation resistors. Each of the isolation resistors of the first set of isolation resistors has one end connected to a first common node, and the other end connected to the second node of one of the first artificial transmission line sections of the first, second, third and fourth cascades of artificial transmission line sections. Each of the isolation resistors of the second set of isolation resistors has one end connected to a second common node, and the other end connected to the second node of one of the second artificial transmission line sections of the first, second, third and fourth cascades of artificial transmission line sections. Each of the isolation resistors of the third set of isolation resistors has one end connected to a third common node, and the other end connected to the second node of one of the third artificial transmission line sections of the first, second, third and fourth cascades of artificial transmission line sections. These resistors may be in the form of a resistive material overlying the ground plane.
A composite amplifier according to another manifestation of the invention includes a first power splitter/combiner including a common port and a plurality of individual ports. The first power splitter/combiner has its common port coupled to receive electromagnetic signals which are to be divided into substantially equal-amplitude portions, and generates substantially equal-amplitude signal portions at each of the individual ports of the first power splitter/combiner. The composite amplifier also includes a plurality of amplifiers equal in number to the number of the plurality of individual ports of the first power splitter/combiner. Each of the plurality of amplifiers includes an output port, and also includes an input port coupled to a corresponding one of the individual ports of the first power splitter/combiner, for receiving at the input port of that amplifier one of the equal-amplitude signal portions. Each amplifier is for generating amplified signals at its output ports. A second power splitter/combiner includes a common port and the same plurality of individual ports. The second power splitter/combiner has each of its individual ports coupled to the output port of one of the amplifiers. The second power splitter/combiner is for combining the amplified signals to produce combined amplified signals at the common port of the second power splitter/combiner. At least one of the first and second power splitter/combiners includes (a) a plurality, equal in number to the plurality, of cascades of artificial transmission lines. Each of the cascades of artificial transmission lines includes an input port and an output port. Each of the cascades of artificial transmission lines also includes at least a first section of artificial transmission line coupled to the input port and has a node remote from the input port, and a last section of artificial transmission line connected to the output port and having a node remote from the output port. Each of the cascades of artificial transmission lines also includes a further coupling arrangement coupling the node of the first artificial transmission line to the node of the last artificial transmission lines. This further coupling arrangement may comprise one of (i) a simple connection of the node of the first section of artificial transmission line to the node of the last section of artificial transmission line and (ii) a further artificial transmission line including input and output nodes, one of which nodes of the further artificial transmission line is connected to the node of the first section of artificial transmission line. The one of the first and second power splitter/couplers also includes (b) an input coupling arrangement coupled to the input ports of the plurality of cascades of artificial transmission lines, for coupling the input ports of the plurality of cascades in parallel to define the common port of the power splitter/combiner. Thus, electromagnetic signals, if applied to the common port of the power splitter/combiner, divide in accordance with the impedances presented by the input ports of the cascades. The one of the first and second power splitter/couplers also includes (c) a plurality, equal in number to the number of stages of artificial transmission line cascaded in any one of the cascades of artificial transmission lines, of sets of equal-valued isolation resistors. One of the sets of equal-valued isolation resistors is coupled to the output ports of the cascades and to a node common to the one of the sets. The resistors of other ones of the plurality of sets of equal-valued isolation resistors are coupled to a node common to the specific other one of the plurality of sets of equal-value isolation resistors, and to those nodes of stages of the artificial transmission lines remote from the input port of that one of the cascade of artificial transmission lines in which the stages of the artificial transmission lines lie. Each of the stages of artificial transmission line, in one hypostasis of the composite amplifier, includes at least first and second planar spiral inductors overlying a ground plane. The first and second planar spiral inductors are electrically coupled in series, and at least one of the artificial transmission lines further including first, second and third discrete capacitors coupled to the spiral inductors. Finally, the one of the splitter/combiners also includes a coupling arrangement for coupling the output port of each of the cascades of artificial transmission lines to one of the individual ports of the splitter/combiner.
In one version of this manifestation, at least some of the discrete capacitors are in the form of a capacitive metallization overlying the ground plane, and separated therefrom by a layer of dielectric material.
A composite amplifier according to a particular manifestation of the invention includes a plurality of amplifiers, each having an input port and an output port, the amplifiers being physically arrayed in a side-by-side line fashion defining a bisector. A common input port is located on the bisector of the line of the array, on that side of the array on which the input ports of the amplifiers lie. A common output port is located on the bisector, on that side of the array on which the output ports of the amplifiers lie. A first conductor structure includes elongated equal-length conductor strips connected to each of the input ports of the amplifiers and to a common point adjacent the common input port, and electrically connected to the common input port. A second conductor structure includes an elongated equal-length conductor strips connected to each of the output ports of the amplifiers and to a common point adjacent the common output port, and electrically connected to the common output port.